U.S. patent number 4,589,487 [Application Number 06/642,029] was granted by the patent office on 1986-05-20 for viscous oil recovery.
This patent grant is currently assigned to Mobil Oil Corporation. Invention is credited to Valadi N. Venkatesan, Paul B. Venuto.
United States Patent |
4,589,487 |
Venkatesan , et al. |
May 20, 1986 |
Viscous oil recovery
Abstract
A method of recovering oil from a subterranean, viscous
oil-containing formation comprising injecting into the formation an
aqueous solution of at least one salt of carbonic acid, and then
recovering the oil from the formation by means of a drive
means.
Inventors: |
Venkatesan; Valadi N.
(Arlington, TX), Venuto; Paul B. (Dallas, TX) |
Assignee: |
Mobil Oil Corporation (New
York, NY)
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Family
ID: |
26990652 |
Appl.
No.: |
06/642,029 |
Filed: |
August 20, 1984 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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337353 |
Jan 6, 1982 |
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Current U.S.
Class: |
166/261;
166/400 |
Current CPC
Class: |
C09K
8/58 (20130101); C09K 8/592 (20130101); E21B
43/243 (20130101); E21B 43/24 (20130101); E21B
43/164 (20130101) |
Current International
Class: |
C09K
8/58 (20060101); C09K 8/592 (20060101); E21B
43/243 (20060101); E21B 43/16 (20060101); E21B
43/24 (20060101); E21B 043/22 (); E21B 043/24 ();
E21B 043/243 () |
Field of
Search: |
;166/256,261,271,272,273,274,275,303,35R,307 ;252/8.55D |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"A Current Appraisal of Thermal Recovery", Journal of Petroleum
Technology, Michael Prats, Aug. 1978, pp. 1129-1136..
|
Primary Examiner: Suchfield; George A.
Attorney, Agent or Firm: McKillop; Alexander J. Gilman;
Michael G. Aksman; Stanislaus
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This is a continuation-in-part of application Ser. No. 337,353,
filed on Jan. 6, 1982, now abandoned, the entire contents of which
are incorporated herein by reference.
Claims
What is claimed is:
1. A method for recovering oil having the gravity of not greater
than about 35.degree. API from a subterranean, viscous
oil-containing formation penetrated by at least one injection well
and at least one spaced-apart production well, both of said
injection and production wells being in fluid communication with a
substantial portion of the formation, consisting essentially of the
following steps in the recited order:
(a) establishing fluid communication between the injection well and
the production well;
(b) injecting into the formation through the injection well at
least 0.20 pore volume of an aqueous solution containing at least
1.0% by weight of at least one water-soluble, inorganic salt of
carbonic acid to form a complex with the oil, thereby increasing
the mobility of the oil, said injecting being conducted for a
sufficient time to provide the residence time of the solution in
the formation of about 2 to 10 days;
(c) initiating an oil drive process in the formation through the
injection well; and
(d) recovering oil from the formation through the production
well.
2. A method of claim 1 wherein said oil drive process consists
essentially of the injection of a driving fluid through the
injection well into the formation.
3. A method of claim 2 wherein the amount of the aqueous solution
injected into the formation during step (b) is about 0.25 to about
0.70 pore volume.
4. A method of claim 3 wherein the aqueous solution contains about
1 to about 10% by weight of at least one water-soluble, inorganic
salt of carbonic acid.
5. A method of claim 4 wherein the aqueous solution contains about
2 to about 6% by weight of at least one water-soluble, inorganic
salt of carbonic acid.
6. A method of claim 5 wherein the driving fluid is carbon
dioxide.
7. A method of claim 6 wherein said at least one salt of carbonic
acid is selected from the group consisting of alkali metal
carbonates, alkali metal bicarbonates, alkaline earth metal
carbonates, alkaline earth metal bicarbonates, ammonium carbonate
and ammonium bicarbonate.
8. A method of claim 7 wherein the salt of carbonic acid is
selected from the group consisting of sodium carbonate, sodium
bicarbonate, potassium carbonate, potassium bicarbonate, ammonium
carbonate, ammonium bicarbonate and mixtures thereof.
9. A method of claim 5 wherein the driving fluid is hot water.
10. A method of claim 5 wherein the driving fluid is steam.
11. A method of claim 5 wherein the driving fluid is a mixture of
steam and carbon dioxide.
12. A method of claim 5 wherein the driving fluid is the production
gas from an in-situ combustion process.
13. A method of claim 5 wherein said driving fluid consists
essentially of a combustion front initiated by an in-situ
combustion operation in the formation by injecting an
oxygen-containing gas into the formation.
14. A method of claim 13 wherein the oxygen-containing gas is
air.
15. A method of claim 13 wherein the oxygen-containing gas is
essentially pure oxygen.
16. A method of claim 13 wherein the oxygen-containing gas is air
enriched with oxygen.
17. A method of claim 13 wherein steam is injected simultaneously
with the oxygen-containing gas during the in-situ combustion
operation.
18. A method of claim 13 wherein water is injected simultaneously
with the oxygen-containing gas during the in-situ combustion
operation.
19. A method for recovering oil having the gravity of not greater
than about 35.degree. API from a subterranean, viscous
oil-containing formation penetrated by at least one injection well
and at least one spaced-apart production well, both of said
injection and production wells being in fluid communication with a
substantial portion of the formation, consisting essentially of the
following steps in the recited order:
(a) establishing fluid communication between the injection well and
the production well;
(b) injecting into the formation through the injection well at
least 0.20 pore volume of an aqueous solution containing at least
1.0% by weight of at least one water-soluble, inorganic salt of
carbonic acid to form a complex with the oil, thereby increasing
the mobility of the oil, said injecting being conducted for a
sufficient time to provide the residence time of the solution in
the formation of about 2 to 10 days;
(c) initiating an oil drive process in the formation through the
injection well;
(d) repeating said step (b) at least once simultaneously with said
step (c), and
(e) recovering oil from the formation through the production
well.
20. A method of claim 19 wherein said oil drive process consists
essentially of the injection of a driving fluid through the
injection well into the formation.
21. A method of claim 20 wherein the amount of the aqueous solution
injected into the formation during step (b) is about 0.25 to about
0.70 pore volume.
22. A method of claim 21 wherein the aqueous solution contains
about 1 to about 10% by weight of at least one water-soluble,
inorganic salt of carbonic acid.
23. A method of claim 22 wherein the driving fluid is carbon
dioxide.
24. A method of claim 22 wherein the driving fluid is a mixture of
steam and carbon dioxide.
25. A method of claim 22 wherein said driving fluid consists
essentially of a combustion front initiated by an in-situ
combustion operation in the formation by injecting an
oxygen-containing gas into the formation.
26. A method of claim 25 wherein the oxygen-containing gas is
air.
27. A method of claim 26 wherein the oxygen-containing gas is air
enriched with oxygen.
28. A method of claim 27 wherein said at least one salt of carbonic
acid is selected from the group consisting of alkali metal
carbonates, alkali metal bicarbonates, alkaline earth metal
carbonates, alkaline earth metal bicarbonates, ammonium carbonate
and ammonium bicarbonate.
29. A method of claim 28 wherein the salt of carbonic acid is
selected from the group consisting of sodium carbonate, sodium
bicarbonate, potassium carbonate, potassium bicarbonate, ammonium
carbonate, ammonium bicarbonate and mixtures thereof.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of recovery of heavy, viscous
oil from subterranean oil-containing formations. More particularly,
this invention relates to an improved tertiary method of recovering
heavy oil, wherein the oil is pretreated with a solution which
increases its mobility and thereafter a drive fluid is used to
displace and recover the oil from the formation.
2. Background of the Invention
There are vast reserves of heavy oil contained in subterranean
formations whose natural characteristics, such as high viscosity,
low API gravity, and high molecular weight render recovery thereof
by primary oil recovery techniques commercially unfeasible due to
the lack of natural reservoir energy. In addition, these reserves
have relatively low permeability although they may have high
porosity.
Attempts have been made in the past to employ known oil
displacement procedures for tertiary recovery of the oil by
injecting fluid through the formation between injection and
production wells. Such attempts include waterflooding, miscible
flooding, chemical or micellar flooding, polymer flooding, thermal
recovery by hot fluid injection, thermal recovery by in-situ
combustion and solvent flooding. Such techniques improve the
mobility of the oil, thereby enhancing the recovery of heavy
oil.
Among these recovery techniques, the miscible flooding process
using carbon dioxide (CO.sub.2) has often been used for enhanced
oil recovery. The CO.sub.2 miscible flooding process is often
applicable to high gravity crude oils, e.g., 25 API, and involves
high operating pressures (starting at about 1500 psi). These
particular conditions under which the process is practiced produce
true miscibility of oil or hydrocarbons with CO.sub.2 thus forming
a single phase, which can be recovered relatively readily from
underground formations.
Attempts were made in the past to employ carbon dioxide for the
recovery of heavy crude oils. Heavy crude oils are classified as
those having a low API gravity and/or high viscosity which are
difficult to produce by ordinary methods of primary and secondary
oil recovery. They also contain very small amounts of low boiling
components. At present, there is an increased interest in the
application of carbon dioxide gas for reducing the viscosity of
heavy oils thus causing a decrease in the effect of viscous forces
associated with the in-situ recovery of heavy oils. However,
preliminary review of the published literature suggests that the
benefit of carbon dioxide in the miscible flooding processes may be
less promising than expected. Even as a dissolved gas, the
application of CO.sub.2 in heavy oil does not look promising
because: (i) the solubility of CO.sub.2 in heavy oils having a low
API gravity is lower than that in light oils, (ii) for pressures
corresponding to reservoir depths of 2000 ft. or below, the
solubility of CO.sub.2 in H.sub.2 O is comparable to that in heavy
crude oil which competitively reduces the effective dissolution of
the CO.sub.2 gas in heavy crude oils, (iii) CO.sub.2 compression
costs for deep reservoirs are excessive, and (iv) the solubility of
CO.sub.2 markedly decreases above 80.degree. C.
One of the most widely used secondary supplemental oil recovery
techniques is waterflooding which involves the injection of water
into an oil-containing formation. As the water moves through the
formation, it acts to displace oil to a production system composed
of one or more wells through which the oil is recovered. It has
also been proposed to add surfactants to the injected water to
lower the oil-water interfacial tension and/or alter the
wettability characteristics of the formation rock to enhance
recovery of the oil. Various surfactant waterflooding techniques
are disclosed in U.S. Pat. No. 3,469,630 to Hurd et al. and U.S.
Pat. No. 3,977,470 to Chang.
Another waterflooding technique is taught in U.S. Pat. No.
3,757,861 to Routson which discloses the introduction into the
formation of an aqueous solution of peroxide, typically hydrogen
peroxide, and thereafter or simultaneously the introduction of an
aqueous solution of alkali metal hydroxides or carbonates or
ammonium hydroxide.
Ralfsnider et al, U.S. Pat. No. 3,532,165 disclose the injection
into an underground formation of a concentrated solution of an
inorganic acid, e.g., hydrochloric or sulfuric acid, followed by
the injection of a stoichiometric excess of a saturated solution of
an inorganic salt, such as sodium carbonate. Alternatively, an
aqueous solution of a sodium carbonate or bicarbonate is injected
into the formation, followed by the injection of sodium sulfite or
bisulfite. Both methods generate in-situ carbon dioxide.
However, there is still a need in the art of recovering heavy oils
(gravity of not more than 20.degree. API) and medium gravity oils
(gravity of 20.degree.-35.degree. API) for improved recovery
techniques which produce higher amounts of such oils than
previously-known methods.
SUMMARY OF THE INVENTION
In accordance with the present invention, the recovery of heavy and
medium gravity viscous oils from a subterranean oil-containing
formation is enhanced by introducing into the formation through an
injection well an aqueous solution of at least one inorganic,
water-soluble salt of carbonic acid capable of forming a complex
with the oil, thereby increasing the mobility of the oil.
Thereafter, an oil drive process, also referred to herein as a
driving means, e.g., injection of a drive fluid, is initiated in
the formation through the injection well to displace the mobilized
oil through the formation toward one or more production wells from
which the oil is recovered.
In carrying out the invention, after fluid communication passages
have been established in a conventional manner between the
injection well and the production well, at least 0.20 pore volume,
and preferably 0.25 to 0.70 pore volume, of an aqueous solution
containing a minimum concentration of about 1.0 percent by weight
of at least one inorganic, water-soluble salt of carbonic acid is
injected into the oil-containing formation through the injection
well. The solution is injected for a sufficient time to provide
residence time of the solution in the formation of about 2 to about
10 days, preferably about 3-5 days. Thereafter, oil is recovered
from the formation by a driving means, such as a drive fluid, e.g.,
hot water, steam, or a combination thereof, miscible drive, such as
carbon dioxide, or a combustion front drive initiated by in-situ
combustion. The drive fluid injected into the formation through the
injection well displaces the mobilized oil through the formation
toward the production well from which the oil is recovered.
Alternatively, the aqueous solution is injected as slugs
alternately with the driving means into the formation. In yet
another alternative embodiment, the aqueous solution is
continuously co-injected into the formation with the driving means
to facilitate enhanced mobility of the oil.
DETAILED DESCRIPTION OF THE INVENTION
The process of the present invention can be used in recovering
heavy oils having gravity of not more than 20.degree. API, as well
as medium gravity oils (having gravity of 20.degree.-35.degree.
API), although it is most applicable to the recovery of heavy
oils.
The aqueous solution contains at least 1% by weight, preferably
from about 1% to about 10% by weight, and most preferably about 2%
to about 6% by weight of at least one inorganic, water-soluble salt
of carbonic acid which forms a complex with the oil of the
formation. The formation of the complex increases the mobility of
the oil and enhances its recovery from the formation through the
subsequent use of the driving means. Both, carbonate and
bicarbonate salts, also referred to herein as carbonates and
bicarbonates, can be used in the process of this invention.
Preferred salts are selected from the group consisting of alkali
metal carbonates, alkali metal bicarbonates, alkaline earth metal
carbonates, alkaline earth metal bicarbonates, ammonium carbonate,
and ammonium bicarbonate. Examples of suitable carbonates are
ammonium, sodium, potassium, rubidium, lithium, cesium, berylium,
barium, magnesium, calcium and strontium carbonates. Examples of
suitable bicarbonates are sodium, potassium, lithium, rubidium,
cesium, ammonium, and francium bicarbonates. The most preferred
salts are selected from the group consisting of sodium carbonate,
sodium bicarbonate, potassium carbonate, potassium bicarbonate,
ammonium carbonate, ammonium bicarbonate and mixtures thereof.
As an illustrative example, a viscous oil-containing formation is
penetrated by at least one injection well and a spaced apart
production well which are in fluid communication with a substantial
portion of the formation through horizontal perforations. The
communication can be established in the formation between the
injection well and the production well using any conventional
means, such as hydrofracturing, explosive means or nuclear means.
Once fluid communication between the injection well and the
production well has been established, at least 0.20 pore volume and
preferably about 0.25 to about 0.70 pore volume, of the aqueous
solution of at least one carbonic acid salt is injected into the
formation through the injection well.
After the desired amount of the carbonic acid salt has been
injected into the formation, a conventional oil drive process is
initiated, such as the injection of carbon dioxide into the
formation, through the injection well to displace the mobilized oil
to the production well from which oil is recovered. The oil drive
process is continued along with the production of oil until the
produced oil contains an unfavorable amount of driving means, e.g.,
carbon dioxide. At this point, production is terminated.
The oil drive process employed after the injection of the solution
of a salt of carbonic acid may include, in addition to carbon
dioxide flooding, hot waterflooding, steam flooding, a mixture of
steam and carbon dioxide flooding, steam stimulation, cyclic steam
stimulation, in-situ combustion using an oxygen-containing gas to
support combustion, production gas mixture recovered from in-situ
combustion process and wet in-situ combustion which includes
simultaneous injection of water and/or steam along with injection
of the oxygen-containing gas. The oxygen-containing gas used for
the in-situ combustion operation may include air, air enriched with
oxygen, or essentially pure oxygen.
In an alternative embodiment, additional amounts of the aqueous
carbonic acid salt solution may be periodically injected into the
formation during the production step, i.e., during the oil drive
process, in an amount of about 0.20 to about 0.25 pore volume in
order to maintain a sufficient amount of the carbonic acid salt in
the formation to mobilize the oil. In yet another alternative
embodiment, once the initial portion of the carbonic acid salt
solution has been injected, injection of the carbonic acid salt
solution may be continued simultaneously with the oil drive process
at a predetermined rate depending upon the characteristics of the
formation and well pattern. In any of the embodiments, the most
preferred driving means is carbon dioxide.
It is significant that the process of the present invention
substantially enhances the recovery of oil from underground
formation without the necessity of injecting into the formation
several chemical agents, e.g., sulfuric acid, followed by the
injection of sodium carbonate, or sodium carbonate or bicarbonate,
followed by the injection of sodium sulfite or bisulfite, as
thought necessary in prior art (e.g., see Ralfsnider et al, U.S.
Pat. No. 3,532,165). Thus, the process of the present invention,
although relatively simple and inexpensive because it relies on the
injection of a solution of relatively easily available and
inexpensive agents, is very effective in enhancing oil recovery,
and particularly heavy oil recovery, from otherwise difficult to
produce subterranean oil deposits.
The chemical or physical mechanism of the process of the present
invention is not understood. However, without wishing to be bound
by any theory of operability, it is thought that the injection, for
the above-identified length of time, into the subterranean
formation of an aqueous solution containing the above-identified
amounts of at least one salt of carbonic acid causes the formation
of a complex with the oil which increases the mobility of the oil
in the formation. Accordingly, subsequent or simultaneous
introduction of the driving means into the formation results in the
recovery of the larger proportion of the oil than the introduction
of the driving means alone. Although it is believed that the
aqueous solution of at least one salt of carbonic acid used herein
increases the mobility of the oil and thus renders it easier to
recover by any means, the process of oil recovery is especially
improved when the injection of the salt of carbonic acid is
combined with the use of carbon dioxide as the driving means. The
carbon dioxide may be injected through the injection well or it may
be generated in situ by the decomposition of the carbonic acid salt
or salts injected into the formation, as illustrated by the
following equation for sodium bicarbonate.
The carbonic acid salt or salts injected into the formation
decompose under the underground deposit's recovery conditions of
this invention.
While the invention has been described in terms of a single
injection well and a single spaced apart production well, the
method of the invention may be practiced using a variety of well
patterns. Any other number of wells, which may be arranged
according to any pattern, may be applied in using the present
process as illustrated in U.S. Pat. No. 3,927,716 to Burdyn et
al.
The term "pore volume" as used herein and in the appended claims is
that volume of the portion of the formation defined by the
injection and production wells, as described in greater detail in
the aforementioned Burdyn et al. patent, the entire contents of
which are incorporated herein by reference.
It will be apparent to those skilled in the art that the specific
embodiments discussed above can be successfully repeated with
ingredients equivalent to those generically or specifically set
forth above and under variable process conditions.
From the foregoing specification, one skilled in the art can
readily ascertain the essential features of this invention and
without departing from the spirit and scope thereof can adapt it to
various diverse applications.
* * * * *